The yield potential of any soybean crop production system can be greatly enhanced by planting as early as possible. Why? There are three reasons:
1. You want your soybean crop to collect as much of the seasonally available solar radiation as possible, simply because plants require the energy of sunlight to convert carbon dioxide into carbohydrates, protein, and lipids (oils).
Clearly, with earlier planting, a soybean crop canopy will cover the ground sooner in the growing season, collecting nearly all of the incoming sunlight from that day forward. Why waste free sunlight by letting it hit the ground? Indeed, the goal each year for a soybean producer is simple: Get that soybean canopy green to the eye by the 4th of July.
Also keep in mind that day length increases from the equal day/equal night cycle of the spring equinox to the longest day/shortest night cycle of the summer solstice. A soybean crop, when planted in late April or early May, is likely to close its canopy within a week or so after the summer solstice. Later-planted soybean crops will be deprived of the opportunity to collect as many hours of sunlight compared to earlier planted crops, and thus will invariably have less yield potential.